On a per app level, i'm not sure it's currently possible short of modifying the app itself.
Judging from the screenshots, the app needs to be updated for holo (the UI theme in android 3.0+) anyway.
On a rom level essentially you want your rom to be themeable.
Roms such as cyanogen mod have a built in theming engine.
If you're rooted and not on a rom that has a theme engine (such as stock), you can use HKThemeManager
Though most themes focus on the holo assets, theming the pre holo assets isnt really a focus for anyone since they're becoming rather rare.
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